Search

International audience; Sound insulation at low frequencies for aerospace and automotive applications is difficult to tackle by using material layers with low density and thickness. Traditional approaches to solve this problem are limited by space and weight constraints. A new approach is needed to achieve the desired acoustic performance with a lower volume, weight and hence less energy required: metamaterials for acoustics applications seem to be a part of the answer. In this work we study the effects of cavities shaped as fractal geometries for the development of Fractal Metamaterials (HFM). The cavities have geometries that obey mathematical formulation covering zero to fifth order scales, as well as geometrical equivalents which are not fractals. Samples are manufactured by 3D printing and tested in an impedance tube. The goal of this work is to evaluate the feasibility of the concept and designing a tool that will allow engineers to use metamaterials in the field of acoustics. The experimental work is performed using a Design of Experiments (DoE) approach, with combinations of design factors and levels of acoustic response considered to identify the interaction amongst independent variables of the metamaterial structure. The experimental results have led to the creation of a performance map that can be used to achieve acoustic insulation with metamaterials. The following work has made use of both numerical and experimental studies to prove a concept and showcase the feasibility of achieving sound insulation with subwavelength materials. The numerical FE simulations broadly agree with the experimental results.